The rosy gene on chromosome III of Drosophila melanogaster is responsible for the biosynthesis of the enzyme, xanthine dehydrogenase (XDH). A large body of genetic data has been accumulated for this region, making it one of the most thoroughly characterized loci of any differentiated organism, from the genetic standpoint. Studies are being carried out to provide biochemical information on XDH to complement the genetic studies, and to extend our knowledge of the rosy region to the molecular level. Experiments are designed to: 1. Determine the location of XDH structural variants on the polypeptide chain by peptide mapping. 2. Provide information of the physical and chemical properties of normal and defective enzymes. 3. Elucidate a partial amino acid sequence of the protein. BIBLIOGRAPHIC REFERENCES: Genetics 84, 233-255 (1976). Organization of the Rosy Locus in Drosophila melanogaster: Evidence for a Control Element Adjacent to the Xanthine Dehydrogenase Structural Element. A. Chovnick, W. Gelbart, M. McCarron, B. Osmond, E.P.M. Candido and D.L. Baillie. J. Supramolec. Struct. Suppl. 1, 55 (1977). Comparison of Kinetic Parameters for Xanthine Dehydrogenase from Wild-Type and from a Putative Regulatory Variant of Drosophila melanogaster. E.P.M. Candido, T.C.R. Edwards and A. Chovnick.